Method and arrangement for interference-protected power supply

ABSTRACT

The invention relates to an interference-protected method and arrangement for supplying power, wherein the power supply between main devices and a masthead preamplifier of a base station in a cellular radio system takes place through an antenna line, and overvoltage formed on the antenna line is conducted to the ground by means of an overvoltage protector adapted for radio frequencies. The use of separate cables and separate overvoltage protector for the supply cable is thus avoided.

This application is the national phase of international applicationPCT/FI96/00580, filed Oct. 30 1996 which was designated the U.S.

FIELD OF THE INVENTION

The invention relates to an interference-protected method for supplyingpower to a receiver in a cellular radio system, said method beingemployed at a base station in a cellular radio system, said base stationcomprising main devices, peripheral devices, and an antenna line betweenthe main devices and the peripheral devices, said main devicescomprising at least a power supply and an antenna filter, and saidperipheral devices comprising at least a masthead amplifier.

The invention also relates to an interference-protected arrangement forsupplying power to a receiver at a base station of a cellular radiosystem, said base station comprising main devices, peripheral devices,and an antenna line between the main devices and the peripheral devices,said main devices comprising at least a power supply and an antennafilter, and said peripheral devices comprising at least a mastheadamplifier.

BACKGROUND OF THE INVENTION

A base station of a cellular radio system comprises an antenna, andtransmitter and receiver means. Since radio frequencies are rapidlyattenuated, distorted and disturbed in conductors, the received signalis usually amplified as close to the antenna as possible. For thispurpose, a masthead preamplifier, which is a peripheral device of a basestation, is employed in the immediate vicinity of an antenna which isincluded in a base station of a cellular radio system and which isusually located in terrain. The main devices of a base station comprise,for example, one or more power supplies for supplying power to thedevices included in the base station. The power supply of a mastheadpreamplifier is typically implemented with low-frequency alternatingcurrent or with direct current by means of a separate power supply cablebetween a power supply included in the main devices of a base stationand a masthead preamplifier. The power supply cable is protected by aseparate, conventional overvoltage protector. It is laborious to mount apower supply cable between the main devices of a base station and amasthead preamplifier. Costs result from both the installation work andthe cable itself. In addition, the overvoltage protector required by thepower supply cable often cannot be sufficiently well implemented andcauses extra work and costs.

CHARACTERISTICS OF THE INVENTION

The object of the present invention is to provide power supply for abase station in such a way that the installation of a separate powersupply cable is avoided and the overvoltage protection is improved.

This is achieved with a method of the type described in theintroduction, which is characterized by supplying operational voltagefrom a main device to a peripheral device of the base station throughthe antenna line, separating the operational voltage supplied on theantenna line and a signal from the antenna from each other in aperipheral device by filtering, and conducting overvoltage formed on theantenna line to the ground through a 1/4 wave length impedance matchingstub operating on the radio frequencies used by the base station.

The power supply arrangement of the invention is characterized in thatthe antenna line is arranged to supply operational voltage from the maindevices to the peripheral devices, the peripheral device comprisesfilter means for separating operational voltage supplied to the antennaline and a signal from the antenna from each other, and the 1/4 wavelength impedance matching stub operating on the radio frequenciesemployed by the base station is arranged to conduct overvoltages to theground.

The method of the invention has significant advantages. The solution ofthe invention allows the number of cables to be reduced, whereby asmaller number of components are needed in the overvoltage protectionand the overvoltage protection is enhanced. This reduces the overallcosts.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be described in greater detail withreference to the examples illustrated in the accompanying drawings, inwhich

FIG. 1 shows the general structure of a base station in a cellular radiosystem, and

FIG. 2 shows an example of the operable coupling of the overvoltageprotector according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a typical structure of a base station in a cellular radiosystem. The base station 10 comprises an antenna 11, a peripheral device12, an antenna line 13, a main device 14 comprising various parts 14asuch as transmitter and receiver blocks, an antenna filter 14b and apower supply 14c of the base station. The antenna filter 14b comprises amain device connector 14d, to which the antenna line 13 is connected. Inthe case of the present invention, the peripheral device 12 is amasthead preamplifier. The operation of the base station 10--which isdescribed herein only from the point of view of reception--connectsparts 11 to 14d to each other in the following manner. After the antenna11 has received a transmitted signal, which may be very weak, the signalis supplied from the antenna to the preamplifier 12. The preamplifier 12should be as close to the antenna 11 as possible to prevent the signalfrom being further weakened. For this reason and because a base stationoften comprises an antenna mast of some kind, the preamplifier 12 ismounted in the antenna mast. From the preamplifier 12, the signal isforwarded to the antenna filter 14b and from there to further processes.The power used by the various devices 12-14b in the base station 10 isobtained from the power supply 14c.

FIG. 2 shows an example of an overvoltage protector of power supply inthe solution of the invention. The arrangement for overvoltageprotection comprises a preamplifier 12, an input terminal 20 ofoperational voltage, a radio frequency choke 21, a high-pass filter 22,a receiver connector 23, a component 25 whose electroconductivitychanges as a function of voltage, a microstrip line 26, ground 27 of thebase station and a main device connector 14d for the base station. Parts14d and 20 to 26 are operationally coupled to one another as follows.The antenna line 13 is connected to the main device connector 14d. Fromthe antenna line 13, a received signal is supplied through the maindevice connector 14d to the microstrip line 26, from which it continuesfurther via the high-pass filter 22 and the receiver connector 23 to thereceiver. The microstrip line 26 connects the main device connector 14d,to which the antenna line 13 leads, and the receiver connector 23. Themicrostrip line 26 is typically a conductor which is provided with auniform ground plane and located on top of an insulator and which guidesthe propagation of electromagnetic radiation. The radio frequency choke21 prevents the propagation of the signal to the power supply throughthe terminal 20.

In the event of interference, overvoltage is generated on the antennaline 13; the overvoltage propagates in the same way as a signal to themicrostrip line 26. In the microstrip line 26, however, the overvoltageis discharged through the overvoltage protector 24, 25 to the ground 27,and thus it does not propagate to the connector 23 nor to the furtherprocesses in the receiver.

In the following, the solution of the invention will be studied moreclosely with reference to FIGS. 1 and 2. In the solution of theinvention, electric power is supplied from a main device 14 of a basestation 10 to a peripheral device 12 via an antenna line 13. Overvoltagegenerated on the antenna line 13 by the action of lightning, forexample, is supplied in the solution of the invention to the ground 27by connecting an impedance matching stub 24 between the antenna line 13and the ground 27 to serve as an overvoltage protector. The impedancematching stub 24 operates on the radio frequencies used by the basestation 10, and its length is λ/4+n*λ/2, where λ is the wavelength, andn is an integer, and n ε [0, 1, 2, . . . ]. In the receiver of the basestation 10, it is always necessary to use an antenna line 13 between themain device and the antenna 11. Since the power supply of a peripheraldevice 12 located in the vicinity of the antenna 11 takes place throughthe antenna line 13, no separate power supply cable is needed, which isan advantage. The peripheral device 12 comprises filter means 12a forseparating the power supply intended as operational voltage from ahigh-frequency signal containing information. The operational voltageenables the operation of the preamplifier 12 and the filters included init. These filter means 12a for separating operational voltage and asignal from each other are filters that operate on radio frequencies andare assembled from integrated circuits or separate components. Theoperational voltage in the solution of the invention is oflow-frequency, typically clearly below 1 kHz, or of direct current.There is no specific limit for the frequency of the operational voltage;however, the frequency band of the operational voltage must be separableby existing filtering methods from interference and from a signal whosefrequency is typically at least dozens of megahertzes. Overvoltagecaused by lightning, for example, has a broad frequency band; for thisreason, the operational voltage should preferably be either normalvoltage of network frequency or direct voltage, in which case powersupply would have a narrow band, which reduces the amount ofinterference in the power supply.

The main device 14 of the base station comprises a microstrip line 26which connects the antenna line and the receiver; radio-frequencyradiation propagates along the microstrip line, and the antenna line 13is operationally coupled thereto. Between a first end of the impedancematching stub 24 and the microstrip line 26, there is provided acomponent 25 which changes its electroconductivity as a function ofvoltage. If the overvoltage protector consists merely of the impedancematching stub 24, direct voltage cannot be used in the power supply ofthe masthead preamplifier 12, since the impedance matching stub 24 wouldthen form a short circuit from the microstrip line 26 to the ground. Toallow direct-current power supply, the component 25 which changes itselectroconductivity as a function of voltage is employed between theimpedance matching stub 24 and the microstrip line 26. Under normaloperating conditions, without any overvoltage on the antenna line 13 andthe microstrip line 26, the impedance of the component 25 is so highthat no significant amount of current is conducted through it to theground 27 of the base station. When the interference voltage increasesin the microstrip line 26, the conductivity of the component 25increases, and the interfering overvoltage is conducted to the ground27.

The component 25 which changes its electro-conductivity as a function ofvoltage is preferably a varistor which operates in a typicallynon-linear manner: as the voltage grows in the microstrip line 26 suchthat it exceeds a predetermined threshold value, the impedance of thevaristor 25 falls abruptly from its normal, very high value and becomesvery low, whereby the high interference voltage is conducted to theground 27 of the base station. The normal impedance of the varistor 25is over 10 megaohms, but with high voltages it falls below 100 ohms. Theimpedance change typically takes place in 10 microseconds with greatvoltage variations. To conduct overvoltage to grounds as rapidly as thisdoes not disturb transition of speech, for example, since a human beingcannot perceive short interruptions. Moreover, particularly in a digitalcellular radio system, error correction can further reduce theinterference caused by a short interruption. The component 25 whichchanges its electroconductivity as a function of voltage can also be azener diode which is preferably a bidirectional protective zener whichgives the same protective properties as the varistor.

The overvoltage protector of the invention is integrated into the unitto be protected in the base station. Typically the protector cuts offovervoltages between ±50 V to 200 V, which is a lower level than what isachieved with the known commercial solutions. The protector conducts acurrent of the magnitude 35 A to the ground. The operational voltage U+is typically a direct voltage of 12 V; in view of sensitive electroniccomponents, it is therefore the better, the lower the overvoltageprotection begins. The overvoltage protection can further be enhanced byusing--in addition to the overvoltage protector of the invention, whichis integrated into the structure--separately installed commercialovervoltage protectors. In this case, the voltage capacity of theprotector can be increased to over 200 V, particularly to provideprotection against a high-energy overvoltage pulse; at the same time,the magnitude of the interference current conducted to the ground maygrow even up to 40 kA. When the solution of the invention is used inconjunction with a commercial overvoltage protector, it protects thedevices of a base station against a residual pulse of a high-energypulse. The operating range of `primary protectors` of commercialovervoltage protectors is from about ±90 V upwards, but even higherresidual pulses are possible. Commercial overvoltage protectors and thesolution of the present invention complement each other.

Although the invention has been described above with reference to theexample illustrated in the drawings, it will be clear that the inventionis not limited to this example, but it can be modified in many wayswithin the scope of the inventive concept disclosed in the appendedclaims.

We claim:
 1. An interference-protected method for supplying power to areceiver in a cellular radio system, said method being employed at abase station (10) in a cellular radio system, said base stationcomprising main devices (14), peripheral devices (12), and an antennaline (13) between the main devices (14) and the peripheral devices (12),said main devices (14) comprising at least a power supply (14c) and anantenna filter (14b), and said peripheral devices (12) comprising atleast a masthead amplifier, characterized by supplying operationalvoltage from a main device (14) to a peripheral device (12) of the basestation through the antenna line (13),separating the operational voltagesupplied on the antenna line (13) and a signal from an antenna (11) fromeach other in a peripheral device (12) by filtering (12a), andconducting overvoltage formed on the antenna line (13) to the ground(27) through a component (25) which changes its impedance as a functionof voltage, and through an impedance matching stub (24) which isconnected thereto and operates on the radio frequencies used by the basestation (10).
 2. A method according to claim 1, characterized in that,as a main device (14) of the base station (10) comprises a microstripline (26) which connects the antenna line (13) and a receiver block(14a) and to which the antenna line (13) is operationally coupled,overvoltage formed on the antenna line (13) is conducted to the ground(24) through a component (25) which is connected to the microstrip line(26) and which changes its impedance as a function of voltage, andthrough an impedance matching stub connected thereto.
 3. A methodaccording to claim 1, characterized in that the length of the impedancematching stub (24) is λ/4+n*λ/2, where λ is the wavelength, and n is aninteger.
 4. An interference-protected arrangement for supplying power toa receiver at a base station (10) of a cellular radio system, said basestation comprising main devices (14), peripheral devices (12), and anantenna line (13) between the main devices (14) and the peripheraldevices (12), said main devices (14) comprising at least a power supply(14c) and an antenna filter (14b), and said peripheral devices (12)comprising at least a masthead amplifier, characterized in that theantenna line (13) is arranged to supply operational voltage from themain devices (14) to the peripheral devices (12),one peripheral device(12) comprises filter means (12a) for separating operational voltagesupplied to the antenna line (13) and a signal from the antenna (11)from each other, and an impedance matching stub (24) operating on theradio frequencies employed by the base station (10) and a component (25)which changes its electroconductivity as a function of voltage arearranged to conduct overvoltages to the ground (27).
 5. A power supplyarrangement according to claim 4, characterized in that, as a maindevice (14) of the base station (10) comprises a microstrip line (26) towhich the antenna line (13) is operationally coupled, a component (25)which changes its electroconductivity as a function of voltage isarranged to be connected between a first end of the impedance matchingstub (24) and the microstrip line (26).
 6. A power supply arrangementaccording to claim 4, characterized in that the length of the impedancematching stub (24) is λ/4+n*λ/2, where λ is the wavelength, and n is aninteger.
 7. A power supply arrangement according to claim 4,characterized in that the component (25) which changes itselectroconductivity as a function of voltage is a varistor.
 8. A powersupply arrangement according to claim 4, characterized in that thecomponent (2) which changes its electroconductivity as a function ofvoltage is a zener diode.
 9. A power supply arrangement according toclaim 4, characterized in that the zener diode is a bidirectionalprotective zener diode.